The present invention relates to a multi-beam scanning device for scanning a plurality of beams respectively emitted by a plurality of light sources toward objects to be scanned.
A scanning device employed in a monochromatic laser printer or the like, which forms an image in accordance with an electrophotographic imaging method, is provided with a laser diode, which is driven in accordance with an image signal. A laser beam emitted by the laser diode is collimated by a collimating lens, deflected by a polygonal mirror within a predetermined angular range, for example, in a horizontal direction. The scanning beam is refracted and converged by an fxcex8 lens, and incident on an object, for example, a photoconductive drum so that the surface of the photoconductive drum is exposed to light in accordance with the image signal, thereby a latent image being thereon.
The latent image is developed as toner is applied. The developed image, i.e., the toner image is transferred onto a recording sheet, and fixed thereon.
A color printer or a color copier, which forms a color image in accordance with the electrophotographic imaging method, is also known. Among various types of color printers or copiers, one employing a scanning device, which is provided with a plurality of light sources for respective color components, is known. Such a scanning device (which will be referred to as a multi-beam scanning device hereinafter) is provided with, for example, four light sources (laser diodes) for yellow, magenta, cyan and black components, and four fxcex8 lenses for respective color components. Four photoconductive drums for the four color components are provided, and the laser beams emitted by the four laser diodes are incident on the four photoconductive drums through the four fxcex8 lenses, respectively. The above-described exposing, developing and transferring procedure of the electrophotographic method are performed for each color component, the four toner images for the four colors are overlaid in the transferring process, and finally, the fixing process is performed for fixing the overlaid toner images of all the color components on a recording sheet.
In the multi-beam scanning device, it is necessary that the distance between the photoconductive drums is relatively long. Downsizing of electrophotographic processing units, such as discharging unit, charging unit, developing unit and transferring unit is limited, and it is preferable that a space surrounding the photoconductive drum is large. Further, it is also preferable that a toner container which supplies toner to the developing unit is large. If the toner container is large, the toner is to be refilled less frequently.
On the other hand, for an optical system including the fxcex8 lenses, it is important that an optical path length from a polygonal mirror to each photoconductive drum should be made as short as possible. If the optical path length is longer, the fxcex8 lens should be made larger, and therefore, the entire device should be made larger.
It is therefore an object of the present invention to provide an improved multi-beam scanning device, in which a distance between objects to be scanned can be made relatively wide, and an optical path length from the polygonal mirror to each object to be scanned can be minimized, and therefore, the entire device can be downsized.
For the above object, according to the present invention, there is provided a multi-beam scanning device, provided with a light source that emits a plurality of light beams, a polygonal mirror that deflects the light beams emitted by the light source to scan, and an optical system that converges the deflected light beams on a plurality of objects to be scanned. The optical system includes an optical path turning system that turns optical paths of the deflected light beams, respectively. The optical path turning system is constructed such that optical path lengths of the optical path of the deflected light beams being the same. In this configuration, one of the optical paths directed to an object located farthest from the polygonal mirror consists of two linear paths and one turning portion at which a beam is deflected.
With this construction, if the optical length of the optical path directing the beam to the farthest object is minimized, the other optical path can easily be adjusted to have the same optical length. Therefore, the distance between the polygonal mirror and each object can be reduced. Further, a sufficient distance between each object can be obtained.
Therefore, the scanning device can be downsized, and sufficient room for arranging the electrophotographic imaging process can be obtained.
Optionally, the optical system includes an fxcex8 lens group including at least a first fxcex8 lens, a second fxcex8 lens and a plurality of third fxcex8 lenses, the number of the third fxcex8 lenses corresponding to the number of the objects, all the light beams deflected by the polygonal mirror passing the first and second fxcex8 lenses, the plurality of light beams passed through the first and second fxcex8 lenses passing respective one of the plurality of third fxcex8 lenses.
In this case, the first fxcex8 lens converges the light beams mainly in an auxiliary scanning direction that is perpendicular to a main scanning direction in which the plurality of light beams scan.
Optionally or alternatively, the second fxcex8 lens converging the light beams only in a main scanning direction in which the plurality of light beams scan.
Further optionally or alternatively, each of the third fxcex8 lenses converging an incident light beam in a main scanning direction where the light beams scan and in an auxiliary scanning direction perpendicular to the main scanning direction.
According to another aspect of the invention, there is provided a multi-beam scanning device, which is provided with a light source that emits a plurality of light beams, a polygonal mirror that deflects the light beams emitted by the light source to scan, and an optical system that converges the deflected light beams on a plurality of objects to be scanned. The optical system includes a plurality of fxcex8 lenses and an optical path turning system that turns optical paths of the deflected light beams, respectively. The plurality of fxcex8 lenses include a first fxcex8 lens through which all of the light beams deflected by the polygonal mirror pass. The optical path turning system is constructed such that optical path lengths of the optical path of the deflected light beams being the same. The plurality of objects being arranged on one side of the polygonal mirror, the plurality of objects being located at different distances from the polygonal mirror, respectively. One of the plurality of optical paths directed to an object located closest to the polygonal mirror includes a portion located between the polygonal mirror and the first fxcex8 lens.
With this construction, a distance between the polygonal mirror and an object closest to the polygonal mirror can be made relatively short, and the objects can be spaced from each other sufficiently. Accordingly, the scanning device can be downsized, and sufficient room for arranging the units necessary for the electrophotographic imaging process can be obtained.
Optionally, the fxcex8 lenses includes at least a first fxcex8 lens, a second fxcex8 lens and a plurality of third fxcex8 lenses. All the light beams deflected by the polygonal mirror pass the first and second fxcex8 lenses, and the plurality of light beams passed through the first and second fxcex8 lenses pass respective one of the plurality of third fxcex8 lenses.
In this case, the first fxcex8 lens may converge the light beams mainly in an auxiliary scanning direction that is perpendicular to a main scanning direction in which the plurality of light beams scan.
Optionally or alternatively, the second fxcex8 lens may converge the light beams only in a main scanning direction in which the plurality of light beams scan.
Optionally or alternatively, each of the third fxcex8 lenses may converge an incident light beam in a main scanning direction where the light beams scan and in an auxiliary scanning direction perpendicular to the main scanning direction.
According to a further aspect of the invention, there is provided a multi-beam scanning device, which is provided with a light source that emits more than two light beams, a polygonal mirror that deflects the light beams emitted by the light source to scan, and an optical system that converges the deflected light beams on more than two objects to be scanned, the number of objects corresponding to the number of light beams emitted by the light source. The optical system includes an optical path turning system that turns optical paths of the deflected light beams, respectively, the optical path turning system being constructed such that optical path lengths of the optical path of the deflected light beams being the same. Further, one of the optical paths includes a portion located on one side of the polygonal mirror, the other of the optical paths located on the opposite side of the polygonal mirror.
With this configuration, one of the objects can be located on one side of the polygonal mirror, and the other objects can be located on the opposite side of the polygonal mirror. Therefore, the distance between the polygonal mirror and each of the objects can be made shorter, and the objects can be arranged to be spaced from each other sufficiently. Accordingly, the scanning device can be downsized, and sufficient room for arranging the units for the electrophotographic imaging process can be obtained.
Optionally, the optical system includes an fxcex8 lens group having a plurality of fxcex8 lenses, the fxcex8 lens group including a first fxcex8 lens, all the laser beams deflected by the polygonal mirror passing through the first fxcex8 lens. All the optical paths located on the opposite side of the polygonal mirror being directed to respective objects, the objects arranged on the one side of the polygonal mirror being located at different distances from the polygonal mirror, respectively. One of the optical paths located on the opposite side of the polygonal mirror directed to one of the objects located closest to the polygonal mirror includes a portion located between the polygonal mirror and the first fxcex8 lens.
In this case, the fxcex8 lenses may include at least a first fxcex8 lens, a second fxcex8 lens and a plurality of third fxcex8 lenses. All the light beams deflected by the polygonal mirror pass the first and second fxcex8 lenses, and the plurality of light beams passed through the first and second fxcex8 lenses pass respective one of the plurality of third fxcex8 lenses.
Further, the first fxcex8 lens may converge the light beams mainly in an auxiliary scanning direction that is perpendicular to a main scanning direction in which the plurality of light beams scan.
Optionally or alternatively, the second fxcex8 lens may converge the light beams only in a main scanning direction in which the plurality of light beams scan.
Optionally or alternatively, each of the third fxcex8 lenses may converge an incident light beam in a main scanning direction where the light beams scan and in an auxiliary scanning direction perpendicular to the main scanning direction.
Further, the first fxcex8 lens may converge the light beams mainly in an auxiliary scanning direction that is perpendicular to a main scanning direction in which the plurality of light beams scan.
Furthermore, the optical system may include an fxcex8 lens group including at least a first fxcex8 lens, a second fxcex8 lens and a plurality of third fxcex8 lenses, the number of the third fxcex8 lenses corresponding to the number of the objects, all the light beams deflected by the polygonal mirror passing the first and second fxcex8 lenses, the plurality of light beams passed through the first and second fxcex8 lenses passing respective one of the plurality of third fxcex8 lenses.
In this case, the first fxcex8 lens may converge the light beams mainly in an auxiliary scanning direction that is perpendicular to a main scanning direction in which the plurality of light beams scan.
Optionally or alternatively, the second fxcex8 lens may converge the light beams only in a main scanning direction in which the plurality of light beams scan.
Optionally or alternatively, each of the third fxcex8 lenses may converge an incident light beam in a main scanning direction where the light beams scan and in an auxiliary scanning direction perpendicular to the main scanning direction.